Helene; One Year Later (Part 1): Early warning signs showed Helene’s potential

By: Lead Forecaster Daniel Crawley

Today, we begin a multi-part series looking back at Hurricane Helene, its evolution and how it turned into the largest natural disaster in the history of western North Carolina replacing major weather events such as the floods of 1916 and 1940.

Between now and Saturday (Sept 27), the official 1-year anniversary, we will look back at the storm from a forecaster’s perspective here at Foothills Weather Network. We will go over the factors that created a three-day rain event that brought historic flooding to many river basins in WNC along with the impact of strong winds as Helene itself moved in. We will also re-live the post-storm impacts that Helene brought to the region, including several of the counties that we cover daily at Foothills Weather Network.

Part 1 of the series starts with a look back at September 22^nd, 2024, which was five days before Helene made landfall. Foothills Weather Network was closely monitoring the tropics during this timeframe as the National Hurricane Center was highlighting the Western Caribbean and Yucatan Peninsula for possible tropical development. Two days prior to that, our weather team posted a blog about the potential of development in that region. NHC officially assigned INVEST 97L to this feature on the 22^nd which helped to initiate hurricane model guidance to help compliment the global models in creating a forecast.

Speaking of the global models, there was a remarkable agreement among the GFS and European Model suites as far a 5-7 days out of gradual development of the feature and then being pulled up into the Gulf. Across North America, it appeared that “future Helene” would be drawn north due to the combination of a closed upper low along the Lower Mississippi River and a Western Atlantic Ridge which prevents this storm to make a hard right toward Florida.

The deterministic and ensembles were lining up well that an area of widespread precipitation would be pulled into the Southeast US. For us here in Western North Carolina, we understand the impact of how tropical moisture can interact with the Southern Appalachians. So as far out as the 22^nd, our interest was definitely high on this storm system.

With the model agreement being higher than normal at the timeframe, the Weather Prediction Center began to highlight parts of the Southeast US for excessive rainfall potential…

Coming Up: In part 2 we dig into the evolution of a “predecessor rainfall event” and how it came about with the forecast of Helene. Part 2 will be available on our website on Tuesday.